I've been using CS 5.1 at work and it will show lines (green and sometimes pink) when it is snapping to other object's alignments.
I use 5.5 at home and layers will still snap to others, but they will not show the line guides, unlike Illustrator that always shows the green lines.

My question is, how would I turn on those green lines/guides? I want to be able to make sure I'm aligning to the right object and not something that's close to it. Is it an add-on? Because I couldn't for the life of me find an option to turn it on/off at home.